Roof and waterproofing membranes and linings have long been used to protect buildings, to contain water in ponds and decorative water features, to prevent leaching of contaminants from landfills, and for other purposes. While these membranes have utility, leakage through the membranes is an ongoing problem. The efforts to contain and locate leakage have resulted in the rise of specialized consultants, air and vacuum testable membranes, and electrical testing methods that not only determine if a leak is present in a membrane system, but where the leak is located.
Detecting water leaks in electrically non-conductive roofing and waterproofing membranes using electronic means has been used for decades. Methods such as those described by U.S. Pat. No. 4,565,965 (hereinafter “Geesen”) and U.S. Pat. No. 7,872,479 (hereinafter “Lorenz”) use a similar method first described by Geesen. The basis of detection in these inventions is that leak location requires a manually held and operated two-pole arrangement to indicate the location of a leak. In the method shown by Lorenz, and referring to prior art FIG. 1, each pole 70 being held at arm's length apart from the other pole 71, measures the electrical field 85 on the surface of the roofing or waterproofing membrane 66 at the point at which the pole touches the membrane or the overburden surface above the membrane if the membrane is under soil, pavers or the like. A measuring unit 69 through which the two poles 70, 71 are connected compares the input of each pole and, via the small amount of current flow from the pole receiving a higher voltage to the pole receiving the lower voltage, indicates which pole has the lower voltage (or the higher voltage, depending on how the mechanism is adjusted) compared to the other pole. This creates an electrical slope 81, 82, 83, 84 that can be detected by the aforementioned procedure. It is water from leakage that contacts the supporting structure of the building or other construction entity 61, located on the underside (below) the membrane that allows these electrical slopes 81-84 to develop as the power source 72 references the structure on one of its terminals. This allows the user of the two-pole method to make judgements as to which direction the electrical field 85 slopes by following the direction of a needle or vector 86 on the measuring unit 69 and to follow that indicated electrical slope to the supposed point of leakage.
While Geesen taught that the structure of the building must be conductive and referenced by one side of the power source for the method to work, Lorenz et. al. in their embodiment, added the provision of an additional layer of conductive material 65 directly under the membrane 66 to which one terminal of the power source 72 is connected as a reference, thus bypassing the conductive structure of the building 61, but achieving the same result of leak location. In this second embodiment, it is claimed that the conductive material 65 positioned directly under the membrane provides a more reliable connection to the power source 72 and thus provides a more reliable test when searching for a leak. FIG. 1 also shows a felt separating layer 64 that is used only to protect the membrane 66 from mechanical damage from the conductive material 65, which may be metal grating.
While Lorenz can be an effective method of leak location, both Lorenz and Geesen have an unaddressed problem that is the basis for this application: the membrane 66 must be non-conductive and remain non-conductive for this method to work effectively. If the conductive properties of the membrane allow more current to pass through it over time when the membrane is exposed to constant moisture or cycles of moisture, the electrical field 85 measured by the two poles 70, 71 can become nearly identical, as the entire surface of the membrane is allowing current to pass through it to the mesh, creating no reliable readings to indicate leakage or false positives.
This electrically permeable membrane can and does occur when the membrane has been exposed to moisture for a period of time, especially when the membrane is buried under green roofing or covered by gravel or pavers. The inventor's experience and subsequent tests with membranes exposed to moisture range from slight degradation of the dielectric properties of the membrane to a membrane that is almost transparent to electrical current for the purposes of scanning the membrane and locating leaks using the above-described electrical method. The materials from which the membranes are manufactured vary in their response to moisture: some membranes, such as thermoplastic olefins (TPO), can hold up fairly well exposed to moisture over time, but membranes such as PVC and Modified PVC membranes (KEE) and several Modified Bitumen membranes lose some of their electrical resistance properties over a similar period of time. Also, the addition of reinforcing in a membrane can also determine some of its electrical resistance characteristics.
To summarize, the system disclosed in Lorenz, which is hereby incorporated by reference, includes at least one conductive metal grating web beneath at least one insulating sealing web with an upper and lower face; at least one voltage source applied between the upper and lower faces of the sealing web and where the metal grating web is connected to a pole of the voltage source; and a test set with two measurement sensors that scans the upper face of the sealing web. Although this system may function as intended in ideal conditions, it has several drawbacks. Most significantly, even insulating membranes, like Lorenz's insulating membrane may be come conductive over time due to moisture vapor transmission. As water gradually permeates the insulating membrane, the conductive web beneath the insulating membrane becomes electrically transparent to any sensing from above and the electrical current can move through the insulating membrane itself.
This phenomena of increased conductivity of insulating membranes has been documented for decades. In the 1950's, for example, Bell Labs noted that high tension wires started arcing after a few years in service. A study was commissioned to find the mechanism that caused this degradation in insulating ability. Ultimately, the study indicated increased conductivity of cable-grade polyethylene exposed to weather over time. Anecdotally, the present inventor performed an informal study whereby he immersed ostensibly insulating membranes in water and then let them dry. A few days later, he tested the membranes and all had become more conductive. If the insulating membranes in systems such as Lorenz become conductive, the voltage detection mechanisms will no longer be able to discern a leaking membrane from a sound membrane.
Therefore there is a need for an improved leak detection and location system that addresses the issue of insulating membranes becoming conductive through exposure.